Smoke detector adapted to a smoke sensing apparatus

ABSTRACT

A smoke detector is disclosed which comprises an inner electrode, an intermediate electrode with a hole for passing radioactive rays therethrough, an outer electrode having openings for allowing smoke to flow therethrough, and one radioactive source, the inner and intermediate electrodes forming an inner ionization chamber, the intermediate and outer electrodes forming an outer ionization chamber, the radioactive source being disposed in the inner ionization chamber. A proper quantity of radioactive rays from the radioactive source is applied into the outer ionization chamber through the hole provided in the intermediate electrode.

RELATED CASE

This application is a continuation of Ser. No. 860,357 filed Sept. 23,1969, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to improved smoke detectors adapted to asmoke sensing apparatus comprising a smoke detector and an electricindicating or alarming device including a relay such as, for example, acontrol electric valve the control electrode of which is connected tothe output terminal of said smoke detector, and more particularly tosmoke detectors in which a kind of radioactive substance is used incommon in two ionization chambers.

Hitherto, as a method of detecting particles contained in any kind ofsmoke, it has been well known to utilize ionization of said particles.For this purpose, a smoke detector provided with two inner and outerionization chambers each including a radioactive substance therein hasbeen generally used, said outer chamber being denoted as an outerionization chamber and being provided with a metal wire net for passingouter gas therethrough, and said inner chamber being denoted as an innerionization chamber and being constructed so that penetration of saidouter gas into said inner ionization chamber is very difficult.

In the conventional smoke detectors as mentioned above, there aredisadvantages such that the detector becomes large in its structure,very complicated in its construction, and uneconomical because each ofthe inner and outer ionization chambers is provided with a radioactivesubstance therein, and, furthermore, the quantity of the radioactiverays is relatively large, thereby increasing harmful effects on humanbodies.

Furthermore, in the conventional smoke detectors as mentioned above,precise detection at various temperature condition or precise detectionunaffected by variation of the surrounding temperature is very difficultand simple temperature compensation or alarming of an emergencytemperature itself cannot be attained. For the purpose of temperaturecompensation of the smoke detectors, various compensating circuitsutilizing any kind of various thermistors have been conventionallyutilized, but these circuits are relatively complex and cause expensivestructure of the smoke detector provided with said circuit.

SUMMARY OF THE INVENTION

It is therefore an essential object of the present invention to provideimproved smoke detectors adapted to a smoke sensing apparatus comprisinga smoke detector and an electric indicating or alarming device the inputof which is connected to the output terminal of said smoke detector, andhaving no disadvantages of the conventional smoke detectors mentionedalready.

Said object and other objects of the invention have been attained,according to the invention, by a smoke detector which comprises outer,inner and intermediate electrodes, said intermediate electrode formingan inner ionization chamber therein and said outer and intermediateelectrodes forming an outer ionization chamber therebetween, andcomprises a radioactive substance provided in a position of said innerchamber to cause ionization in said chambers.

The objects, characteristic features and function of the invention willbe described in detail in conjunction with the accompanying, in whichthe same or equivalent members are designated by the same referencenumerals and characters.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic side view, in section, for showing the principleof an example according to the invention;

FIG. 2 is a sectional side view for showing another example of theinvention, corresponding to FIG. 1;

FIG. 3 is a sectional view for showing a further example of theinvention, corresponding to FIG. 1;

FIG. 4 is graph showing the relation between output voltage deviation ΔEof the device, as illustrated in FIGS. 1, 2 or 3, and the surroundingtemperature;

FIGS. 5 and 6 are schematic side views, partly in section, of otherexamples of the invention, respectively; and

FIG. 7 is a plan view showing a part of a modification of the exampleillustrated in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

One example of the invention as illustrated in FIG. 1 comprises aninsulating support member 4 made of a synthetic resin having a largeelectrical resistance, a metal wire net 1 functioning as an outerelectrode, an intermediated electrode 2 supported by a projecting wall4a of the member 4, an inner electrode 3 made of a radioactivesubstance, and an inner electrode supporting member 5 provided with awasher 6 and nuts 7, said outer and intermediate electrodes forming anouter ionization chamber 1a and an inner ionization chamber 2a beingformed at the position inside said intermediate electrode. Theintermediate electrode 2 is provided with at least one small hole A or amembrane (not shown) which is permeable to any radioactive raytherethrough. The examples of the invention, including the example ofFIG. 1, relate to only the case in which only one small hole is providedin the intermediate electrode 2. Furthermore, in the example of FIG. 1,the inner electrode 3 itself is made of a radioactive substance, but aradioactive substance may be attached onto a separately provided innerelectrode, or the intermediate electrode may be made of a radioactivesubstance or may be provided with a radioactive substance attachedthereto. Of course, a radioactive member may be provided at a positionin the outer ionization chamber, with the same effect as the othercases. In the example of FIG. 1, the intermediate electrode is in theform of a circular plate, but said electrode may be replaced by a linearelement or elements.

The operation of the example of FIG. 1 will now be described below.

The detector is designed so that when the atmosphere surrounding thedetector is in normal condition, the output voltage E_(o) between theintermediate electrode 2 and the outer electrode 1 does not energize asmoke sensing apparatus which is not shown, said apparatus comprising asmoke detector to be improved by use with this invention and an electricindicating or alarm device, the input of which is connected to outputterminals of said smoke detector. The said indicating or alarm devicecan be provided with an electric valve having a control electrode whichis energized by abnormal energy produced in the smoke detector, butsince said indicating or alarm device is ordinarily a conventional oneand has no direct relation to the inventive concept of the invention, adetailed description of said device is herein omitted. When a firebreaks out and smoke containing particles therein enters the ionizationchamber 1a through the meshes of the outer electrode 1, ionized air ionsproduced by ionization of the air due to the radioactive substance inthe chamber 1a are adsorbed on said smoke particles thereby to causerecombination of the ions, or these smoke particles absorb radiationenergy of the radioactive substance so as to disturb the ionization,said adsorption and absorption being caused by the extremely largedimension of said smoke particles in comparison with that of the airparticles, whereby the ion current flowing through the ionizationchambers is decreased relative to that in the normal condition, and theelectric potential at the terminal m, that is, the voltage E_(o) isremarkably increased. Accordingly, the smoke sensing apparatus can bemade to operate by said increased voltage E_(o). The fine hole A of theintermediate electrode 2 is adapted to disturb penetration of the smokeparticles into the inner ionization chamber 2a, but to facilitateefficient radiation of radioactive rays into the ionization chamber 1a.Accordingly, the constructions of said members can be modified withinthe concept mentioned above. In the above case, the voltage-currentcharacteristic of the ion current is determined depending upon thestrength of the radioactive substance, dimensions and structures of theelectrodes and the like. Furthermore, for the purpose of compensatingfor the effects caused by the surrounding conditions such astemperature, moisture and atmospheric pressure, it is preferable thatthe outer ionization chamber directly sensing the smoke has anunsaturated characteristic with respect to the ion current, and theinner ionization chamber has a characteristic saturatable at arelatively low voltage, said inner ionization chamber exhibiting highresistance to infiltration of the smoke thereinto, but being freelycommunicated with the outer air.

The example of FIG. 2 is substantially the same as that shown in FIG. 1,except that the inner electrode 3 made of a radioactive substance has apin-shaped form and projects centrally into a hole B provided in theintermediate electrode 2, and the projecting wall 4a in FIG. 1 isreplaced by a side wall 2b of the intermediate electrode 2.

The example of FIG. 3 is substantially the same as that of FIG. 2 exceptfor the structure of the intermediate electrode 2.

According to the examples of FIGS. 1, 2 and 3, a radioactive member isutilized in common for the inner and outer ionization chambers, and theinner ionization chamber is provided inside the outer ionizationchamber, so that the detector is miniaturized and can be manufactured atlow cost.

In the example as illustrated in FIGS. 1 to 3, operation of the detectoris affected by the surrounding temperature, so that precise smokedetection at a certain temperature or generation of an indication oralarm at a particular temperature cannot be attained unless sometemperature compensating method is adopted. According to the invention,however, the devices as illustrated in FIGS. 1 to 3 can be effectivelymodified so as to have none of the disadvantages mentioned above, forexample, by constructing the intermediate electrode from a material thecondition of which is varied in response to temperature variation,adjusting automatically the relative distance between the intermediateand inner electrodes, varying automatically the position of the innerelectrode having the radioactive substance, or adjusting the distancebetween the intermediate electrode and outer electrode, thereby tocompensate irregularity of sensitivity with respect to the surroundingtemperature. Furthermore, for the purpose of operating the smokedetector at a particular temperature, the detector can be designed sothat it may be operated upon deviation of the distance between theintermediate electrode and the inner electrode or the outer electrodefrom a limit value, or it may be operated when radiation of theradioactive rays into the outer ionization chamber is cut off at aspecific temperature.

In the example of FIG. 1, deviation ΔE_(o) of the electric voltage E_(o)with respect to the surrounding temperature is shown in FIG. 4. Thisrelation has been experimentally confirmed by the inventor of thepresent invention. The deviation ΔE_(o) mentioned above can becompensated according to the example illustrated in FIG. 5, in which thesame numerals as those in FIG. 1 designate the same members as those inFIG. 1. However, in the example of FIG. 5, the intermediate electrode ismade of a material such as, for example, a bimetal the condition orposition of which can be varied in response to temperature variation,and the inner electrode 3 is provided with a radioactive substance 3aattached thereto, without itself being made of said substance.

In the example of FIG. 5, if the temperature-responsive property of theintermediate electrode 2 is selected so that the relative distancebetween the intermediate and inner electrodes 2 and 3 may beautomatically adjusted so as to compensate for the variation of thesurrounding temperature, a constant smoke detecting sensitivity can bealways obtained irrespective of the surrounding temperature. In thiscase, when the intermediate electrode is moved so as to decrease therelative distance between the intermediate and inner electrodes, lowtemperature compensation is achieved. On the contrary, when theintermediate electrode is moved so as to increase the relative distancementioned above, high temperature compensation is achieved.

For the sake of operating the detector illustrated in FIG. 5 uponelevation of the surrounding temperature to a certain temperature, forinstance, 70°C, the intermediate electrode 2 is designed so that saidelectrode 2 is moved by a necessary distance a way from the innerelectrode 3 in either an abrupt or gradual manner, thereby to increasethe voltage E_(o) up to a value sufficient to operate the smoke sensingapparatus, not shown.

FIG. 6 shows a modification of the example of FIG. 5. In the case of theexample of FIG. 6, the inner electrode 3 is supported on its supportmember 5 by means of the thermally responsive element 9 so as to bemoved up and down, said support member 5 being passed through theinsulating member 8 held by the insulating support member 4. The element9 is made of, for example, a bimetal and designed to compensate for theinfluence caused by variation of the surrounding temperature. In theexample of FIG. 6, an adjusting screw, not shown, adapted to adjust thesensibility of the element 9 can be provided, or the end face 5a of thesupport member 5 and a contact 10 confronting said end face 5a andsupported by an arm 10a can be utilized for signalling by alarm aspecific emergency temperature, for example, 70°C, by inserting said endface 5a and contact 10 in the circuit of an alarm device of the smokesensing apparatus, not shown.

The examples of FIGS. 1 to 3 can be modified so that the detector may beoperated at a specific temperature. For this purpose, for example, sucha mechanism as shown in FIG. 7 is additionally provided in the detector,said mechanism comprising a bimetal 11 attached at its one end to theintermediate electrode 3 by means of a support pin 11a and provided atits other end with a shield plate 13. If the bimetal 11 is designed sothat when the temperature becomes a predetermined specific value, saidbimetal 11 is turned in the direction of the arrow so as to shut thehole A of the intermediate electrode 3, whereby penetration ofradioactive rays into the outer ionization chamber is stopped and theion current flowing through said chamber disappears, the voltage E_(o)shown in FIG. 1 is abruptly increased at said specific temperature,thereby to operate a control electric valve, not shown.

I claim:
 1. An ionization-type smoke detector comprising: an innerelectrode provided with a radioactive source; an intermediate electrodehaving at least one through-hole; and an outer electrode having openingsthrough which smoke can enter; said inner electrode and saidintermediate electrode forming an inner ionization chamber in which saidradiation source is arranged, said intermediate electrode and said outerelectrode forming an outer ionization chamber, said inner ionizationchamber being arranged inside said outer ionization chamber, and whereina necessary quantity of radioactive rays emitted from said radioactivesource is introduced directly into said outer ionization chamber throughsaid holes.
 2. A smoke detector as defined in Claim 1, in which saidinner electrode is movable upwardly and downwardly.
 3. A smoke detectoras defined in Claim 1, in which said inner electrode is moveableupwardly and downwardly.
 4. A smoke detector as defined in Claim 1, inwhich said inner electrode is supported on a supporting member having anannular projecting wall, and wherein said intermediate electrode issecured to said annular projecting wall.
 5. An ionization-type smokedetector, which comprises: an inner ionization chamber; an outerionization chamber within which said inner chamber is positioned; anintermediate electrode common to both of said chambers and forming aboundary therebetween; an inner electrode positioned within said innerchamber; an outer electrode defining the outer boundary of said outerchamber and having openings therein through which smoke can freely pass;said inner electrode being provided with a radioactive source positionedwithin said inner chamber; said intermediate electrode includingaperture means formed therein for substantially preventing smoke fromentering said inner chamber from said outer chamber and for facilitatingthe passage of radiation from said inner chamber into said outer chamberin order to improve the ionization efficiency therein, said aperturemeans comprising an unobstructed hole formed through said intermediateelectrode.
 6. The smoke detector as set forth in Claim 5, furthercomprising: an insulating support member having an annular wallprojecting therefrom at a position inwardly of the outer circumferencethereof; said intermediate electrode being secured to said annular wallsuch that the inner surfaces thereof define said inner ionizationchamber; the portion of said support member outside said annular wallforming a boundary for said outer ionization chamber; said outerelectrode being secured to the outer circumference of said member.